putExtra treeMap 返回 HashMap 不能转换为 TreeMap android [英] putExtra treeMap returns HashMap cannot be cast to TreeMap android

问题描述

我需要你的帮助，我不明白发生了什么?

I need your help, I cannot understand what's happening?

我正在尝试在 2 个活动之间发送 TreeMap，代码如下:

I'm trying to send a TreeMap between 2 activities, the code is something like this:

class One extends Activity{
 public void send(){
   Intent intent = new Intent(One.this, Two.class);
   TreeMap<String, String> map = new TreeMap<String, String>();
   map.put("1","something");
   intent.putExtra("map", map);
   startActivity(intent);
   finish();
 }
}

class Two extends Activity{
  public void get(){
  (TreeMap<String, String>) getIntent().getExtras().get("map");//Here is the problem
  }
}

这返回给我 HashMap 不能转换为 TreeMap.什么

This returns to me HashMap cannot be cast to TreeMap. What

推荐答案

作为@Jave 建议的替代方案，如果您确实需要将数据结构设为 TreeMap，只需使用相应的构造函数即可另一个地图作为数据源.所以在接收端(Two)做这样的事情:

As alternative to @Jave's suggestions, if you really need the data structure to be a TreeMap, just use the appropriate constructor that takes another map as data source. So on the receiving end (Two) do something like:

public class Two extends Activity {
    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        TreeMap<String, String> map = new TreeMap<String, String>((Map<String, String>) getIntent().getExtras().get("map"));
    }
}

但是，根据您的项目，您可能不必担心确切的 Map 实现.因此，您可以改为转换为 Map 接口:

However, depending on your project, you probably don't have to worry about the exact Map implementation. So in stead, you could just cast to the Map interface:

public class Two extends Activity {
    @Override public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Map<String, String> map = (Map<String, String>) getIntent().getExtras().get("map");
    }
}

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